<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        a{
            text-decoration: none;
        }
        .big {
             position: relative;                 
            width: 150px;
            height: 100px;
            border: 2px solid #000;  }
        .small {
            position: absolute;                       
           left: 50%;
            top: 50%;         
             transform: translate(-50%,-50%);                   
            width: 100px;
            height: 50px;
            background-color: blue;   }
    </style>
    <script>
       alert("hello world")
    </script>
</head>
<body>
    <a href="https://www.baidu.com"></a>
   
</body>
  <div class="big">
    <div class="small"></div>
</div>
</html>
